The invention relates to dot matrix type line printers and, more particularly, dot matrix line printers that include a plurality of hammers formed by the tines of a "comb" that is oscillated back and forth along an axis that lies perpendicular to the axis of movement of the print paper.
Various types of line printers have been proposed and used. One type of line printer that has been found particularly well suited for use as an on-line or off-line remote terminal or direct hookup device includes a comb that is oscillated back and forth in a direction perpendicular to the direction of paper movement. The comb includes a base and a plurality of vertically oriented tines. The tines form the print hammers. Located near the outer end of each hammer is a print anvil, which may be in the form of a ball welded to each hammer. Located on the side of the comb remote from the anvil side are a plurality of print coils. One print coil may be dedicated to each hammer. The hammers are moved back and forth, i.e., in a direction perpendicular both to the direction of oscillatory movement of the comb and perpendicular to the direction of paper movement, by the selective energization of the print coils. Energization of the print coils causes the hammers and, thus, the anvils to be withdrawn. Release of the stored strain energy in the hammers causes the anvils to press a ribbon against the print paper and create a dot thereon. A row/column series of dots formed in this manner create alphanumeric (or other types of) characters. A printer of this general nature is the Series 2000 Line Printer sold by the Tally Corporation, Kent, Wash. A more detailed general description of dot matrix line printers, is set forth in U.S. Pat. Nos. 3,768,403 and 3,782,278, both assigned to Tally Corporation.
While line printers of the type described in the foregoing paragraph have found widespread use as intermediate speed printers, attempts to increase the speed of such printers have not been as successful as desired. One problem that has been particularly difficult to overcome is the sideways vibrational hammer motion (e.g., vibratory hammer motion parallel to the direction of comb motion) that occurs as speed is increased. This sideways vibrational motion is due not only to dynamic forces, but also to magnetic cross-talk between print coils and adjacent print hammers not associated with a given coil during the print operation. As a result, the print hammers do not track in a straight forward-and-back motion, i.e., straight toward and away from the ribbon and paper. Sideways vibrational motion has the undesirable effect of causing the printing of dots that are out of position with respect to an ideal dot print matrix, particularly as printing speed is increased. As a result, the printed characters are not as clear and readable as desired.
Various suggestions have been made to solve the foregoing problem; however, these attempts have been unsuccessful for various reasons. In many cases, while they solved the sideways vibrational motion problem, they caused other print problems. For example, while the installation of caps on hammer tips that fill the space between adjacent hammers or the insertion of a silicone rubber adhesive across the hammer face, reduce or eliminate sideways vibrational motion, they caused other print problems. As a result, such solutions to the sideways vibrational motion problem are unacceptable. Another proposed solution was to bond print hammers and their associated dampers together to increase print hammer sideways rigidity. However, this technique seriously adversely affects print quality. As a result, this proposed solution is also unacceptable. The present invention is directed to overcoming the sideways vibrational motion problem without causing other problems.
It is an object of this invention to provide a mechanism for preventing or substantially reducing the sideways vibrational motion of the hammers of a line printer including a plurality of parallel hammers that are oscillated back and forth during printing.
It is another object of this invention to provide a new and improved hammer mechanism for a line printer.
It is yet another object of this invention to provide a mechanism for greatly reducing or entirely eliminating the sideways vibrational motion of a flexible member without impeding back and forth motion in a direction perpendicular to the direction of sideways motion.